The overall goal of this study is to evaluate mechanisms leading to insomnia in the elderly. This is a common complaint in this age group. About 10% of elderly have long-lasting frequent insomnia (difficulty sleeping). Our study is directed at investigating underlying mechanisms. We will imploy of case-control study. Specifically we will recruit elderly subject with long-lasting insomnia (cases) and subjects with no or rare insomnia in the previous one year (controls). The fundamental hypothesis on which our study is based is that age-related changes in the sleep and circadian processes are major risk factors for insomnia and compound the effect of sleep disorders and somatic diseases that interrupt sleep. Our specific aims are the following: 1) determine the relative role of physiological changes with age (phase advance of the circadian clock, reduced melatonin levels, decrease in EEG slow wave activity) in causation of insomnia; 2) determine whether sleep disorders (sleep apnea and nocturnal myoclonus) are risk factors for insomnia in the elderly; 3) determine whether physiological changes in homeostatic sleep drive an/or the circadian system augment the effects of sleep or somatic disorders that interrupt sleep in the elderly.